The present invention relates generally to mobile communications networks and, more particularly, to a lightweight communications protocol for reducing the number of over-the-air data transactions in mobile subscriber sessions.
The popularity of SIP (Session Initiation Protocol) as a communication protocol has greatly increased in recent years. SIP is modeled after HTTP (HyperText Transfer Protocol), the underlying protocol used by the World Wide Web, and is widely expected to revolutionize telecommunications similar to the way HTTP revolutionized the web. SIP has roots in the wire line broadband world where the driving requirement was to create a loose and flexible protocol that was access independent and generic. Because of the flexible nature of the protocol, standard bodies have begun adopting SIP as a communication protocol on user endpoints. Bandwidth requirements and transaction rates however have not been emphasized.
Mobile networks are undergoing the transformation and migration from the 2G standard to the 3G standard. 3G enables high speed data access to the mobile endpoints, thus opening the doors to many multimedia services. However, although 3G offers high speed data access, it is heavily oversubscribed, i.e., the users/channel ratio is very high (greater than 100 in some markets compared to 5 typically in wireline networks). Heavy oversubscription is primarily caused by the high startup cost in setting up a mobile access network. This high oversubscription significantly reduces the effective bandwidth available to mobile users and network throughput.
By way of example, a typical SIP call flow for VIM (voice instant messaging) is now described. The bandwidth requirements and transaction exchange rate is quantified for a typical VIM session setup and an instant message delivery.
A SIP client has to register with a SIP registrar/server if it wishes to be reached. The registration is valid for a configured time (e.g., one hour) and has the client's network address included in the registration. If at anytime the client changes its network address (e.g., as a result of roaming), it has to re-register with its registrar.
FIG. 1 shows a typical call flow of a SIP client registering with a SIP registrar or server. This procedure is invoked if any change in the mobile network address is made or after some configured time period ends, whatever comes first. Exemplary transactions in a registration procedure shown below require 1 KB.
Via: SIP/2.0/TLS 10.0.33.241:5061;branch=z9hG4bKnashds7 Max-Forwards: 70 From: XXXXX <sips:XXXXX@10.0.33.241>;tag=a73kszlfl To: XXXXX <sips:XXXXX@10.0.33.241> Call-ID: 1j9FpLxk3uxtm8tn@10.0.33.241 CSeq: 1 REGISTER Contact: mailto:XXXXX@vzw.com Authorization: Digest username=“XXXXX”, realm=“boston.vzw.com”,  qop=“auth”, nonce=“1cec4341ae6cbe5a359ea9c8e88df84f”,  opaque=“”, uri=“sips:ss2.vzw.com”,  response=“71ba27c64bd01de719686aa4590d5824”  Content-Length: 0SIP/2.0 200 OK Via: SIP/2.0/TLS 10.0.33.241:5061;branch=z9hG4bKnashds7 ;received=10.0.33.241 From: XXXXX <sips:XXXXX@10.0.33.241>;tag=a73kszlfl To: XXXXX <sips:XXXXX@10.0.33.241>;tag=34095828jh Call-ID: 1j9FpLxk3uxtm8tn@10.0.33.241 CSeq: 1 REGISTER Contact: <sips:XXXXX@10.0.33.241>;expires=3600 Contact: <mailto:XXXXX@vzw.com>;expires=4294967295 Content-Length: 0
Once the registration is performed, the SIP client can transmit and receive messages over the network. FIG. 2 shows an exemplary call flow for a SIP client originating a VIM message. In this example, the SIP call flow takes a total of 5.25K Bytes and 9 SIP transactions to deliver one VIM message.
A fully loaded SIP application server chassis can typically serve 20,000 media ports. Using the standard oversubscription model, such a configuration can serve up to 2,000,000 subscribers. At a 0.02 erlang traffic per subscriber and an average individual message of 10 seconds, the total number of VIM messages the SIP application server will handle is 24,000,000/day or 1,000,000/hour. Using the results from the SIP call flow of 9 SIP messages per VIM, such a configuration will result in 9,000,000 SIP transactions per hour utilizing a total bandwidth of 5.25 G Bytes of SIP message data (overhead). These numbers show that extending SIP to mobile terminals is not efficient in mobile networks; hence improvements for increasing throughput in such an environment would be desirable.